1. Field of the Invention
The present invention relates to an inductor, and more particularly, to a symmetrical inductor.
2. Description of the Prior Art
An inductor is a passive electronic component that stores energy in the form of a magnetic field, and an inductor tends to resist any change in the amount of current flowing through it. The inductor is usually used with capacitors in various wireless communications applications for providing stable currents, switched phases, filtering and resonance. In its simplest form, the inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns, the thickness, the length and the radius of the coil. The inductance also depends on the type of material around which the coil is wound. In a semiconductor manufacturing process, at least two metal layers with specifically designed layout patterns and a plurality of contact plugs for connecting these two metal layers are used to form a wire loop, thus fabricating an inductor onto an integrated circuit chip.
Referring to FIG. 1, FIG. 1 is a schematic diagram of an inductor according to the prior art. As shown in FIG. 1, a differential inductor 10 includes a first metal layer, which consists of a first conductive segment 12 and a second conductive segment 14. The first conductive segment 12 and the second conductive segment 14 are interlaced with each other to form an approximate circle pattern with two overlapping regions A and B. The inductor 10 further includes a second metal layer, which consists of a third conductive segment 20 and a fourth conductive segment 24. The third conductive segment 20 is disposed under the overlapping region A of the first conductive segments 12 and the second conductive segment 14, and the fourth conductive segment 24 is disposed under the overlapping region B of the first conductive segments 12 and the second conductive segment 14. The inductor 10 further includes a dielectric layer (not shown) disposed between the first metal layer and the second metal layer, and a plurality of contact plugs 16, 18, 22, 26 penetrating through the dielectric layer to connect the first metal layer and the second metal layer. For example, the portions of the second conductive segment 14 and the third conductive segment 20 at the overlapping region A are connected with each other via the contact plugs 16 and 18. The portions of the first conductive segment 12 and the fourth conductive segment 24 at the overlapping region B are connected with each other via the contact plugs 22 and 26.
The inductor 10 cannot provide a symmetrical structure at the overlapping regions of the first conductive segment 12 and the second conductive segment 14. For example, at the overlapping region A, the second conductive segment 14 connects to the third conductive segment 20 via the contact plugs 16, 18, however, the first conductive segment 12 does not need any contact plugs to connect to the second metal layer. At the overlapping region B, the first conductive segment 12 connects to the fourth conductive segment 24 via the contact plugs 22, 26, however, the second conductive segment 14 does not need any contact plugs to connect to the second metal layer. In this case, different parasitic resistance values occur in the asymmetrical inductor 10, and two differential signals (V+, V−) at the two ends of the inductor 10 become asymmetrical to result in phase differences and phase noises, thus deeply affecting the electronic circuit characteristics.